JPS6345242B

PURPOSE:To enable automatic control in a filtering operation in the stage of filtering waste water by a precoating type filtering device by measuring the differential pressure between the liquid to be filtered and filtrate before and behind a filter body and optimizing the flow rate of the liquid to be filtered. CONSTITUTION:A filter aid suspended in water is fed to the filter body 1c of a filtering device 1 to deposit the filter aid on the surface of the body 1c. Waste water pump 3 is then run to feed waste water to the device 1 to filter the same. The clean water is taken through a conduit 11 to the outside. The process for cleaning up the waste water is segmented to three stages, i.e. the 1st control stage of a control mode at a constant flow rate, the 2nd control stage of a control mode under the constant differential pressure before and behind the body 1, and the 3rd control stage of a constant flow rate mode. The flow rate of the liquid to be filtered is automatically controlled in each control stage and the transfer to each control stage is also automatically accomplished, whereby laborious manual and monitoring operations are abolished and the stable filtering operation is performed with the less number of precoating treatment for the body 1c.